Photoionization of Electronically Excited Oxygen: Rate of the Reaction O2(a1Δg)+O3→2O2+O

The photoionization spectrum of discharged oxygen has been obtained in the wavelength region 1040–1240 Å with an argon continuum light source and a 1‐m Seya‐Namioka scanning vacuum‐ultraviolet monochromator in a discharge‐flow experiment. Photoionization was detected only at wavelengths shorter than or equal to 1118.0 Å. The observed ion current is due to photoionization of metastable O₂(a ¹Δ_g), and the effects on the ion current of adding O₂, N₂, and O₃ to the flow stream after the discharge are reported. O₂ and N₂ do not reduce the photoionization current except by small percentages attributable to dilution effects and, with added O₂, to a slight absorption of the incident light flux. O₃, however, sharply reduces the ion current and is partially decomposed by the discharged gas. These effects are attributed to the reaction ${\mathrm{O}}_2{\mathrm{(a}}^1{\Delta }_g\mathrm{)+}{\mathrm{O}}_3\text{→2}{\mathrm{O}}_2{\mathrm{(X}}^3{\Sigma }_g^{-}\mathrm{)+}\mathrm{O}{(}^3\mathrm{P)}$ . Measurements of the reduction in photoionization current as a function of added O₃ pressure and reaction time were made, and the rate coefficient for this reaction at room temperature has been found to be (2–3)×10⁻¹⁵ cm³ molecule⁻¹·sec⁻¹. This is a lower value than has been estimated from discharge‐flow experiments in which the metastable species responsible for ozone decomposition could not be identified. Possible reasons for the discrepancy are discussed.